In an X-ray CT apparatus, it is known that sensitivity change of an X-ray detector due to its temperature influences projection data. Specifically, because sensitivity of an X-ray detector changes depending on its temperature, an X-ray CT apparatus is configured to image an object at a stable state of temperature of its X-ray detector and to correct projection data of the imaged object by using preliminarily prepared correction data.
Therefore, when imaging of an object is performed with an X-ray CT apparatus, temperature of its X-ray detector is stabilized by carrying a current from two to four hours before start time of imaging in order to stabilize the temperature state of the X-ray detector.
Here, depending on the hospitals, energization is performed from several hours before start of imaging by using a timer in many cases. Moreover, an X-ray CT apparatus is used by energizing the X-ray detector consecutively for twenty-four hours in designated emergency hospitals, emergency lifesaving centers, etc. in many cases.
Meanwhile, as to methods of generating the correction data used for correcting sensitivity of X-ray data, technology related to a correction data generating method, in which correction data based on phantom data are generated at a predetermined base time point and new correction data are generated so as to reflect temporal change on the previously generated correction data, is disclosed (see Japanese Patent Application Laid-open Publication No. 2007-135749, for example).
Incidentally, hospitals, which have selected to perform energization by using a timer, cannot deal with unscheduled examination such as emergency cases, and thus such hospitals are unavoidably constrained to change their system to energize the X-ray detector consecutively for twenty-four hours in many cases. On the other hand, there have been many demands that power supply to the X-ray detector should be stopped during nighttime and the X-ray detector should be energized only during imaging in terms of saving power.
Here, as a case where the X-ray detector influences projection data, it is known that artifact such as a ring etc. occurs if radiographic data obtained by imaging are corrected with the use of correction data preliminarily prepared at an unstable state of temperature of the X-ray detector.
Therefore, under the state where the temperature of the X-ray detector is not stable, satisfactory projection data can be obtained by the following two steps. The first step is to generate correction data in accordance with temperature state of the X-ray detector, and the second step is to correct the radiographic data obtained through imaging at the time of the first step by using the correction data generated in accordance with the temperature state of the X-ray detector.
However, the temperature of the X-ray detector rises in accordance with elapsed time after start of imaging of an object. Thus, accurate correction cannot be performed by correcting radiographic data with the use of the generated correction data. In addition, because setting conditions of the generated correction data are different from the latest conditions as the temperature of the X-ray detector becomes more stable, artifact occurs in the result even if the radiographic data are corrected by the generated correction data.